This application is based on and claims the benefit of German Patent Application No. 00400265.5 filed Jan. 28, 2000, which is incorporated by reference herein.
The invention relates to a process for the continuous production of longitudinally seam-welded and corrugated metal tubes, the method comprising the steps of forming a metal band drawn off from a supply reel into an open-seam tube, welding the tube at its longitudinal edges, and corrugating the welded smooth tube by engaging the smooth tube by a withdrawal apparatus driven by an electric motor and corrugating the smooth tube by means of a corrugation plate located in a rotationally driven corrugation head. The invention further relates to an apparatus for the continuous production of such metal tubes, the apparatus including a supply reel for a metal band, a forming apparatus forming the metal band into an open-seam tube, a welding apparatus welding the open seam of the open-seam tube, a withdrawal apparatus driven by an electric motor and engaging the welded metal tube, and a corrugation apparatus which has a rotationally driven corrugation head with a corrugation plate, located in the interior of the corrugation head, which forms the corrugation in the smooth tube.
DE-A-16 52 990 discloses a device for the continuous corrugation of thin-walled, in particular longitudinally seam-welded, smooth tubes in which a metal band drawn off from a supply reel is formed into an open-seam tube, welded at its longitudinal edges, and fed to a corrugation apparatus in which the welded smooth tube is provided with a corrugation in the form of a helix. The corrugation apparatus consists of a housing in which, coaxial to the smooth tube running through, a corrugation head is disposed so that it can be driven rotationally. In the corrugation head a corrugation roller ring is mounted so that it is freely rotatable, eccentric to the smooth tube, and of smaller inclination than the pitch of the helix, said corrugation roller ring rolling on rotation of the corrugation head on the surface of the smooth tube and thereby forming the wall of the smooth tube.
The rotational drive of the corrugation head is coupled via a gear mechanism to a withdrawal apparatus with which the smooth tube is transported. The corrugation head is fastened to the hollow shaft, which carries on its outer surface a toothed wheel which engages with a pinion of a toothed gearing. The toothed gearing is coupled via a continuously regulatable gearing to a main drive motor which simultaneously drives the withdrawal apparatus.
With such an apparatus it is possible in a continuous mode of operation to produce metal tubes corrugated in the form of a helix or annulus.
Due to the large encircling mass of the corrugation head and the hollow shaft, the speed of rotation of the corrugation head and thus the rate of production for the corrugated metal tube is naturally relatively low.
DE-A-20 49 235 discloses another corrugation apparatus, wherein a rotationally driven corrugation head is provided which, as described above, can be driven via a hollow shaft, toothed gearing, continuously regulable gearing, and an electric motor. A corrugation tool is mounted in the corrugation head, the tool having a deformation rib which generates the corrugation. The deformation rib has a curve in the form of a helix and its clear width is smaller than the outer diameter of the smooth tube. During the corrugation process, the deformation rib is, so to speak, screwed onto the smooth tube and forms a corrugation in the form of a helix in the wall of the tube. This corrugation technology is used principally for the production of high-frequency cables. However, the same drive is used, and the apparatus therefore suffers from the same disadvantages described above.
An object of the present invention is thus to improve the prior-art corrugation processes and corrugation apparatuses, with the aim of reducing the encircling mass and thereby increasing the rotational speed of the corrugation head to thereby permit a higher rate of production to be achieved.
This object is realized by a process for the continuous production of longitudinally seam-welded and corrugated metal tubes, the method comprising the steps of forming a metal band drawn off from a supply reel into an open-seam tube, welding the tube at its longitudinal edges, and corrugating the welded smooth tube by engaging the smooth tube by a withdrawal apparatus driven by an electric motor and corrugating the smooth tube by means of a corrugation plate located in a rotationally driven corrugation head, said method characterized by the fact that the corrugation head is driven directly by a hollow shaft motor.
The object of the invention is further realized by an apparatus for the continuous production of longitudinally seam-welded and corrugated metal tubes, said apparatus comprising a supply reel for a metal band, a forming apparatus forming the metal band into an open-seam tube, a welding apparatus welding the open seam of the open-seam tube, a withdrawal apparatus driven by an electric motor and engaging the welded metal tube, and a corrugation apparatus which has a rotationally driven corrugation head with a corrugation plate, located in the interior of the corrugation head, which forms the corrugation in the smooth tube, wherein said corrugation head is driven by a hollow shaft motor rotor formed as a tube.
The significant advantage of the invention is that by the use of a hollow shaft motor the number of rotating machine elements in the corrugation apparatus can be reduced to a minimum. The moment of inertia of the rotating elements is reduced to the moment of inertia of the hollow shaft or the rotor of the hollow shaft motor. An increase of the control speed of the drive system results which leads to an improvement of the quality of the corrugated tube. In particular, if the corrugated tubes are used for high-frequency transmission, for example, as hollow conductors or as inner and/or outer conductors of a coaxial high-frequency cable, a uniform form of the corrugation leads to a reduction of the height of reflection points as well as to a reduction of the level of reflection.